1. Field of the Invention
The present invention relates to a process and an apparatus for assembling tyres.
In more detail, the invention applies to the process and equipment used for building a green tyre, to be subsequently submitted to a vulcanisation cycle so as to obtain the final product.
2. Description of the Related Art
A tyre for vehicle wheels generally comprises a carcass structure including at least one carcass ply having respectively opposite end flaps in engagement with respective annular anchoring structures integrated into the regions usually identified with the name of “beads” and having an inner diameter substantially corresponding to a so-called “fitting diameter” of the tyre on a respective rim.
Associated with the carcass structure is a belt structure comprising one or more belt layers, arranged in radially superposed relationship relative to each other and to the carcass ply, provided with textile or metallic reinforcing cords having a crossed orientation and/or disposed substantially parallel to the circumferential extension direction of the tyre. At a radially external position to the belt structure, tread band is applied which is also of elastomeric material like other constituent semifinished products of the tyre.
Respective sidewalls of elastomeric material are further applied, at an axially external position, to the side surfaces of the carcass structure, each extending from one of the side edges of the tread band until close to the respective annular anchoring structure to the beads. In tyres of the “tubeless” type, an airtight coating layer usually referred to as “liner” covers the inner surfaces of the tyre.
Subsequently to building of the green tyre obtained through assembly of the respective components, a vulcanisation and moulding treatment is generally carried out which aims at determining structural stabilisation of the tyre through cross-linking of the elastomeric compounds as well as at impressing it with a desired pattern and with possible distinctive graphic marks at the sidewalls.
The carcass structure and belt structure are generally made separately from each other at respective work stations, to be mutually assembled at a second time.
In more detail, manufacture of the carcass structure first contemplates application of the carcass ply or plies onto a building drum, to form a so-called substantially cylindrical “carcass sleeve”. The annular anchoring structures to the beads are fitted or formed on the opposite end flaps of the carcass ply or plies that are subsequently turned up around the annular structures so as to enclose them in a sort of loop.
A so-called “outer sleeve” is made on a second or auxiliary drum, said outer sleeve comprising the belt layers applied in radially superposed relationship with each other, and possibly the tread band applied at a radially external position to the belt layers. The outer sleeve is then picked up from the auxiliary drum to be coupled to the carcass sleeve. To this aim, the outer sleeve is disposed coaxially around the carcass sleeve and then the carcass ply or plies are shaped into a toroidal configuration, for example by mutual axial approaching of the beads and simultaneous admission of fluid under pressure into the carcass sleeve, so as to cause radial expansion of the carcass plies until adhesion of the latter against the inner surface of the outer sleeve.
Assembly of the carcass sleeve to the outer sleeve can be carried out on the same drum as used for making the carcass sleeve, in which case reference is made to a “unistage building process” or “unistage process”.
Also known are building processes of the so-called “two-stage” type, in which a so-called “first-stage drum” is used for making the carcass sleeve, while assembly between carcass sleeve and outer sleeve is carried out on a so-called “second-stage drum” or “shaping drum” onto which the carcass sleeve picked up from the first-stage drum and subsequently the outer sleeve picked up from the auxiliary drum are transferred.
By the term “elementary semi-finished products” herein and in the following it is intended to denote continuous elongated elements of elastomeric material, textile and/or metallic rubberised cords, strip-like elements. It is to be pointed out that, to the aims of the present specification, by “strip-like element” it is intended a strip of elastomeric material cut to size, comprising one or more textile or metallic reinforcing cords. These elementary semi-finished products lend themselves to be used in an appropriate amount for composing one or more of the above described constituent elements of the tyre, without storage of semi-finished products being required.
EP 1 312 462 discloses a building system in which a ply feeding station, a carcass-building station, an assembly station and a belt building station provided with the respective drums are arranged along a production line. Transport members movable along the production line carry out transfer of the articles of manufacture under processing from a work station to another one, removing the article of manufacture from a drum and disposing it on the drum of the following station.
WO 2004/041521 in the name of the same Applicant discloses a building process in which a carcass sleeve is formed on a primary drum, while a belt structure is made on an auxiliary drum. A tread band is subsequently formed on the belt structure and afterwards the outer sleeve made up of belt structure and tread band is picked up from the auxiliary drum to be coupled to the carcass sleeve disposed on the primary drum. To this aim, a transfer ring places the outer sleeve to a coaxially centred position around the carcass sleeve, and the latter is shaped into a toroidal configuration so as to determine assembly of same with the outer sleeve.
EP 1 481 791 discloses a tyre production system comprising a plurality of carcass-building stations distributed to a predetermined mutual distance to form the carcass structures on respective carcass-building drums sequentially transferred along a carcass-building line. Along a belt production line, formation of the belt structures equipped with the tread band is provided on respective belt building drums sequentially moved between belt building stations distributed to a predetermined mutual distance. Carcasses and belts are mutually assembled inside a vulcanisation mould.
In WO 2006/064526 in the name of the same Applicant, a substantially cylindrical carcass sleeve is provided to be made in a building station, while in a finishing station an outer sleeve is formed which is substantially cylindrical too and comprises a tread band applied at a radially external position to a belt structure. Manufacture of the outer sleeve contemplates that in a first work position of the finishing station a first belt structure is formed on a first auxiliary drum, while in a second work position of the finishing station the tread band is applied to a second belt structure previously formed on a second auxiliary drum. The first auxiliary drum is then positioned to the second work position, while the second auxiliary drum is positioned in a grip position to be picked up by a transfer member to be transferred to a centred position around the carcass sleeve formed in the building station.